1. Field of Disclosure
The present disclosure of invention relates to a reactor for solid ammonium salt, a method of controlling the reactor, and a NOx emission purification system using solid ammonium salt and selective catalytic reduction. More particularly, the present disclosure of invention relates to a reactor for solid ammonium salt, a method of controlling the reactor, and a NOx emission purification system using solid ammonium salt and selective catalytic reduction, used for purifying nitrogen oxide (NOx) which is a harmful exhaust gas exhausted from an internal combustion engine or a combustor. In the NOx emission purification system, the solid ammonium salt such as ammonium carbamate (NH2COOCH4), ammonium carbonate ((NH4)2CO3) and so on is thermally decomposed to be ammonia, and the ammonia is reacted with NOx in the selective catalytic reduction to be purified into nitrogen harmless to human beings.
Description of Related Technology
Generally, exhaust gas recirculation (EGR) or selective catalytic reduction (SCR) is applied to reduce nitrogen oxide exhausted from the internal combustion engine especially for a diesel engine. In the EGR, density of nitrogen oxide is reduced. In SCR, nitrogen oxide is reacted with a catalyst using a reducing agent like ammonia, urea or hydrocarbon, and thus nitrogen oxide is deoxidized into nitrogen and oxygen.
In a HC-SCR technology which is one of the SCR, hydrocarbon like diesel is used as the reducing agent, and thus an additional providing device for the reducing agent is unnecessary. However, oxygen within an exhaust gas and hydrocarbon are reacted, and thus the reduction of NOx is not effective.
In a urea SCR technology which is another technology of the SCR, liquid urea made of melting solid urea in a normal temperature in water, is injected into an exhaust line of a vehicle. The liquid urea injected into the exhaust gas is thermally decomposed into ammonia, and the ammonia deoxidizes nitrogen oxide into harmless nitrogen using selective catalytic reduction like V2O5 or zeolite. Nitrogen oxide is efficiently purified in a wide range of temperature in the urea SCR technology, and the urea SCR technology has high durability.
However, a massive social infrastructure is necessary to provide liquid urea, and additional devices like a container 30 and an injector 40 are necessary, for the urea SCR technology. In addition, a freezing point of the liquid urea is −11° C. and additional heat insulation is necessary to maintain systems like the container and the injector under the temperature, and thus overall system may be complicated. Further, more than 60% water is mixed to the liquid urea is used to decrease the freezing point of the liquid urea, and thus the container for the liquid urea may be increased.
As the technology to solve the above-mentioned problem in the urea SCR technology, Korean Patent Number KR10-0924591 and Korean Patent Number KR10-0999574 disclose the technologies of using solid urea. However, the solid urea is thermally decomposed at about 140° C. and thus electric energy or exhaust heat energy is needed much more, and urea is solidified in a duct line when the temperature for thermal decomposition is not maintained in the duct line or the reactor.
Further, Korean Patent Number KR10-1185413 discloses the technology of using the solid urea having a relatively lower temperature for the thermal decomposition. However, as illustrated in FIG. 1, the reactor 1 storing solid ammonium salt 10 is entirely heated by a heater 20 or a heat exchanger 30 using an exhaust heat or a coolant of the vehicle, to thermally decompose the solid ammonium salt to ammonia, and thus amount of the energy used in the process is increased.